This invention relates to a high density large scale inregrated (LSI) package for logic circuits for use in data processing and communications systems.
LSI packages for logic circuits are indispensable to realize faster and more compact systems. Especially, packages having active elements such as transistors require a structure to diffuse the heat generated by electric power consumption. A multi-chip package having such a heat diffusing structure is proposed in a paper by Hajime Nakamura et al. entitled "Manufacturing Technology of High Circuit Density Multi-Layer Substrates", IEEE, TRANSACTIONS ON COMPUTERS, HYBRIDS, AND MANUFACTURING TECHNOLOGY, VOL. CHMT-4, No. 2, June 1981 issue, pp. 333-337.
The substrate of the package illustrated in FIG. 10 of this paper on page 337 is composed of an alumina ceramic. Multiple signal wiring layers and a power bus layer are formed on the surface of the substrate. An IC ship mounted over the substrate is connected to these wiring layers. To the undersurface of the substrate is stuck a heat sink for diffusing the heat from the IC chip.
The multi-layer wiring substrate of this structure has the following disadvantages.
(1) As each of the insulating layers among the multiple wiring layers, printed and baked inorganic dielectric paste of glass ceramic type is used. The relative dielectric constant .epsilon.r of inorganic dielectric paste usually ranges between 8 or 9. Accordingly, the signal propagation delay time td per unit length of the signal wiring formed on this insulator is calculated from ##EQU1## (where C is the velocity of light, which is 3.3.times.10.sup.10 cm/sec) to be 9 nanoseconds (ns)/m. Thus the signal propagation delay time of this wiring is more than double that of usual coacial cables, which is 4 ns/m.
(2) The conductor wiring layers are formed, for instance, of gold paste, by screen printing. As a result, the wiring width and wiring pitch can be no smaller than 50 microns and 100 microns, respectively.
(3) The heat generated by the IC chip is diffused to the heat sink on the other side through the alumina ceramic substrate. Since the alumina ceramic substrate usually is about 2 mm thick to be strong enough to endure the fabricating stress given for the conductive and dielectric layers due to the temperature change in the process of manufacturing a whole substrate the heat from the IC chip is prevented by the thick alumina substrate from being efficiently diffused to the heat sink.
(4) A heat sink is stuck to the under surface of the substrate all over, so that it is impossible to form input and output terminals on that under surface when input and output terminals are needed for the multi-chip package. Therefore, such input and output terminals must be formed on the upper surface of the alumina ceramic substrate, or the surface on which the wiring and IC chip are mounted. However, since the wiring and IC chip are mounted on that upper surface, terminals cannot be provided on the whole surface of the substrate. Accordingly, this multi-chip package has the disadvantage of being unable to allow the formation of many input and output terminals.